Patent GB-286773-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1926-12-07
Abstract: 286,773. Automatic Telephone Manufacturing Co., Ltd., and Saville, W. Dec. 7, 1926. Automatic telephone systems. - Conference facilities for certain subscribers in a private exchange are obtained by the initiating subscriber first dialling a conference number to obtain connection to a special connector and then dialling special code digits for the required subscribers in turn in any order, the connector automatically returning to normal after each subscriber answers or if one is busy. The conference number raises a group-selector to a special level which is connected both to the conference line bus-bar and to the connector. When a subscriber, reached by means of his special code digit, answers, a special relay, individual to his line, is energized to connect him to the conference line. and the connector automatically returns to normal. Any subscriber can withdraw from the conference by hanging up, and if the initiating subscriber hangs up, any other entitled subscriber can enter the conference by dialling the conference number only. The conference connector may be single-motion or two-directional, according to the number of subscribers for whom facilities are required. If a non-entitled subscriber dials the conference number, he gets the busy signal; the line switches of such subscribers have a special earthed discriminating wiper, the bank contacts of which are connected to the group-selector test-wipers through post-springs operated at the conference level, so that the selector rotates to its eleventh contacts and sends back the busy signal. Some subscribers may be connected to the conference line, but have discriminating wipers in their line switches, so that they may be brought into, but cannot initiate, a conference. The calling party dials the conference number which connects him to the relay group RG. Relays A, B pull up, and when the code number of the conference party is dialled, the rotary magnet SM of the switch RS is operated to step the wipers 20 - - 24 to the required contacts. Relay C is energized while impulsing is in progress, and in turn energizes relay E. After impulsing relays C, E de-energize in turn and the called subscriber's line switch is busied over armatures 2, 4, 15, and wiper 24. Ringing current is now connected to the called line (GEN., lower winding of F, armatures 13, 8, 17, wiper 22, called line, wiper 23, armature 9. and battery). When the called 'party answers. relay F operates and locks up, disconnects ringing current, and operates relay L, which locks up over the called line and switches the. called subscriber through to the conference leads CL, CL<1>. A homing circuit for the switch RS is now completed over wiper 20 and armatures 10, 6, 2, and the switch returns to normal. When the calling partv dials another digit, relay F is de-energized by the operation of armature 4. If the wanted line is busy, relay G energizes over armature 5 and wiper 24 before relay C releases, and locks up over armatures 15, 4, 2. The armatures 4 of relay C is released before armature 5. Busy tone is now connected over armature 16 to the. lead PL and a homing circuit for the switch RS is formed over wiper .20, and armatures 14. 6. 2. Although relay G operates when the wiper 24 passes over a busy contact, it will not lock up nor will the homing circuit be completed, since relays C, E are energized. The called subscribers are connected to the conference leads through condensers C<1>, C<2>. so that each called party can release himself.